"Health experts lamented a move by U.S. President Barack Obama to halt rules on limiting smog pollution, saying the decision could endanger many people already susceptible to respiratory problems.

Under pressure from businesses and Republican lawmakers, the Environmental Protection Agency had delayed issuing a rule on ozone limits several times. On Friday, Obama unexpectedly told the EPA to withdraw the clean-air initiative. Even at current levels, doctors and public health groups warn that ozone, a key smog ingredient, is harmful, especially for those already suffering from lung diseases."

"'We don't really know what level of ozone is truly safe,' said Dr. Monica Kraft, director of the Asthma, Allergy and Airway Center at Duke University and president-elect of the American Thoracic Society.

'We are concerned that there won't be any change (in standards) until 2013, even though the levels we have now already can actually worsen lung disease and cause more symptoms, visits to the emergency departments and deaths.'"